Reflective displays are commercially important in product areas that include electronic readers (e-Readers) and electronic shelf labels. However, current reflective displays lack the performance of color printing on paper. Electrofluidic displays (EFDs), which were introduced in 2009, can provide vivid color, high brightness, and fast switching in a reflective display. Due to its unbeatable color performance, electrofluidic displays provide a solution for future e-paper technology. But due to its specific pixel structure and two different fluids, electrofluidic displays need a novel dosing and sealing technology.
Liquid crystal displays (LCDs) incorporate assemblies that are filled with only a single fluid - a liquid crystal fluid. Traditionally, the liquid crystal fluid has been filled into a LCD by first creating a cavity assembly between two plates, where the perimeter of the plates is sealed with the exception of providing a fill port. The structure is then subjected to vacuum to remove gases from the cavity assembly and thereafter dipped in a liquid crystal pool to allow liquid crystal to occupy the cavities between the plates. In addition, the plates may be subjected to a pressurized environment to drive liquid crystal into the cavities.
With extreme demand for the large LCD panels, this industry started using vacuum based ‘drop’ fill processes. In a drop fill liquid crystal process, drops of liquid crystal are placed upon a first plate (bottom plate) in vacuum at a precisely measured volume, and then a second plate (top plate) is positioned and bonded to the first plate to sandwich the cavity assembly therebetween, all in vacuum.
LCDs may be fabricated using liquid filling, but LCDs do not utilize two immiscible fluids and fail to address any of the problems associated with moving a first fluid (polar or nonpolar) over a second fluid (opposite of the first fluid) without displacing it. LCDs purposely avoid low temperature because the liquid crystal becomes too viscous to fill (fill time increased exponentially with decreasing temperature). Accordingly, these LCD processes cannot be adapted for EFDs.
In contrast to LCDs, EFDs and electrowetting displays (EWDs) require at least two immiscible fluids. During device fabrication, these two fluids, one being polar, and one being non-polar, must be loaded into a display module and then the display module is sealed. The surface energy of the materials, combined with the surface energy of the coatings in the display structure, the properties of the sealant, and the need to omit air bubbles from the display pose a significant technical challenge.
For EWDs, multiple dosing technologies have been reported. Researchers from University of Cincinnati reported self-assembled oil dosing technique utilizing the low surface tension of a colored nonpolar fluid. For this oil dosing process, the device is submerged into a polar fluid, and then a colored nonpolar fluid is injected by needles and then filled into pixels resulting from surface tension. Likewise, an ink-jet printing technique has been demonstrated to inject a colored nonpolar fluid into pixels on one plate, followed by covering the nonpolar fluid with a transparent polar fluid and capping the assembly with a top plate. Accordingly, EWD dosing processes always result in the colored nonpolar fluid filling a microwell. But, for EFDs, just the opposite is the case—a polar fluid must fill the microwell. Moreover, LCDs and EWDs do not involve filling cavities having a dimension in the range of tens of micrometers with individual fluids bodies, and consequently do not encounter air entrapment in small cavities, cleaving the fluid body to keep the ink in the cavities, or enhanced evaporation of the fluid due to its small radius of curvature.
Consequently, there is a need in the art for dosing techniques applicable to EFDs that provides for a reasonable cost display or shutter. More specifically, there is a need for dosing and sealing technologies that provide a reasonable cost manufacturing method for fabricating displays with two liquids inside, wherein one liquid is specifically placed into features, and no air is trapped in the device.
The invention will be further appreciated in light of the following detailed description and drawings, in which: